The present invention relates to a solid state laser having a laser diode as its light source for excitation and, particularly, to a compact solid state laser resonator having a non-linear optical crystal therein.
U.S. Pat. No. 4,942,582 issued on Jul. 17, 1990 to Kintz et al. discloses a basic construction of conventional solid state laser excited by a laser diode. In the solid state laser, a laser resonator is constituted with an output mirror and a laser medium. The outside surface of the laser medium is coated with a reflective film. When the laser medium is optically excited by an output light from the laser diode, a newly excited fundamental wavelength of the laser medium is amplified by the laser resonator and emitted from the output mirror. Generation of second harmonic of the fundamental wavelength is achieved by arranging a non-linear optical crystal such as TKP between the laser medium and the output mirror.
However, the laser medium and the non-linear optical crystal may degrade laser oscillation efficiency when temperature increases. Further, since organic optical crystal may be deliquescent, its characteristics is varied considerably with time when used under atmospheric condition and its life is very short.